Which country did Germany invade in 1939, prompting the UK to declare war?

Okay, so thinking about the start of World War II, it's crucial to remember the sequence of events. In the 1930s, Hitler's Germany was expanding its territory, and European powers were trying to avoid war through appeasement. However, Hitler's ambition couldn't be contained. The invasion of Poland on September 1, 1939, was the final straw. Britain and France had pledged to defend Poland if it was attacked. Two days later, on September 3, after Germany ignored an ultimatum to withdraw, Britain declared war on Germany. This marked the official beginning of World War II. While Germany had annexed Austria earlier in 1938, and later invaded France in 1940, it was the invasion of Poland that directly triggered Britain's declaration of war, making it the pivotal event. Finland, while involved in conflicts with the Soviet Union during the war, wasn't the catalyst for Britain's entry into the conflict.